This program of research seeks to identify the behavioral and psychological functions mediated by the hippocampus and attempts to determine how the hippocampus is functionally integrated with brainstem, hypothalamus and neocortex in the regulation of behavior. By means of electrical stimulation and reversible cryogenic blockade of brainstem-hypothalamic systems, stimulation of which causes contrasting types of electrical patterns in the hippocampus (theta rhythm or desynchronization), we will manipulate the state of hippocampal activity and determine the effect upon the performance of trained behaviors and upon the different stages of sleep and wakefulness. The trained behavioral performances will involve putative hippocampal functions such as visual discrimination tasks in which the role of attention can be minimized or maximized, delayed response tests in which the role of short-term memory can be investigated, and operant behavior in which voluntary motor response and motivational factors can be assessed. Electrophysiological activity in hippocampus and at representative cortical sites will be recorded during performance of the behavioral tasks. Additional investigation of the organization of brainstem and diencephalic systems which influence the hippocampus will be carried out in acute preparations. Overall these studies are believed to have both basic and applied significance. Basically, the results will contribute to a better understanding of the role of the hippocampus and related brain structures in the control of brain electrical activity and in the regulation of behavior. The results should also have application to mental and behavioral disorders associated with the limbic system of which the hippocampus is an important part. Such disorders range from psychosomatic syndromes to the hallucinatory disturbances which characterize psychotic episodes, from hyperactivity and behavioral disorders in children to unmotivated lethargic states of passivity. BIBLIOGRAPHIC REFERENCES: Wilson, C.L., Uryvaev, Y.V. and Lindsley, D.B. Diencephalic stimulation sites affecting hippocampal and neocortical electrical activity in cats. Fed. Proc., 1976 (in press). Wilson, C.L., Motter, B.C. and Lindsley, D.B. Influences of hypothalamic stimulation upon septal and hippocampal electrical activity in the cat. Brain Research, 1976, 104, (in press).